Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of the display screen or portion thereof with a graphical user interface showing the design of FIG. 1 with certain broken line features removed for clarity.

The outermost broken line rectangle illustrates a display screen or portion thereof. The remaining broken lines illustrate portions of the graphical user interface. None of the broken lines form part of the claimed design.

The different shades of gray shown in the Figures depict a contrast in appearance. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 